Went direct without a direct box!

Sounded much better than the direct out from my Carvin R600. Plug the guitar cable right into one on the instrument input jacks on a yamaha mixer. Although some notes seemed boomy it may have just been the room. Anyone else done this?

That should be fine if the mixer is not too far away. And active basses should be able to feed quite long lines without problems. How did you get the signal to your Carvin or were you only using monitors?

A direct box primarily converts your unbalanced instrument signal to a balanced signal. This lets you run a longer cable without loss of quality and with less risk of added noise. If you're close to the mixer you can very well connect directly to it instead. It may sound better than with a low quality direct box, but will perhaps not work if you use a really long cable. For larger gigs or stages where you use a stage box and multi cable (when the mixer and sound guy is located out in the audience for instance) you can't use an instrument cable. I also find it convenient to convert everything to balanced signals as you can then use the same type of microphone cables for all channels, both for amps and for mics. The boominess is probably just a matter of adjusting the EQ to suit the room.